Hydrogen production by partial oxidation of methane: Modeling and simulation

A one-dimensional non-isothermal model for oxygen permeable membrane reactor has been developed to simulate the partial oxidation of methane to produce hydrogen. The performance of two fixed bed reactors (FBRs) viz. one with pure O₂ in feed (FBR1), other with air in feed (FBR2), and a membrane reactor (MR) having air in non-reaction side have been studied at various feed conditions and inlet temperatures in order to investigate the effect of these parameters on conversion of methane and yield of hydrogen. The fixed bed reactor with pure O₂ in feed has been found to provide better performance as compared to fixed bed reactor with air and membrane reactor.     

Hydrogen production over Ni/ceria-supported catalysts by partial oxidation of methane

The catalytic performance of Ni dispersed on ceria-doped supports, (Ce_0.88La_0.12) O_2-x, (Ce_0.91Gd_0.09) O_2-x, (Ce_0.71Gd_0.29) O_2-x, (Ce_0.56Zr_0.44) O_2-x and pure ceria, was tested for the catalytic partial oxidation of Methane (CPOX). The catalysts were characterized by Brunauer Emmett Teller (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) and temperature programmed oxidation (TPO). Ni/ (Ce_0.56Zr_0.44) O_2-x showed higher Hydrogen production than the Ni/Gadolinium-doped catalysts, which may be due to its higher reducibility and surface area. By enhancing the support reducibility in Ni/doped-ceria catalysts, their catalytic activity is promoted because the availability of surface lattice oxygen is increased, which can participate in the formation of CO and H₂. It was also found that Ni/(Ce_0.56Zr_0.44) O_2-x showed higher catalytic performance after redox pretreatments. Similarly, a higher amount of H₂ or O₂ was consumed during hydrogenation and oxidation pretreatments, respectively. This may be correlated to re-dispersion of metallic particles and changes on the metal-support interface. In addition, it was observed that the ionic conductivity of Ni/(Ce_0.56Zr_0.44) O_2-x had an effect on the amount of carbon formed during the CPOX reaction at oxygen concentrations lower than the stoichiometric required, O/C ratios lower than 0.6. Its high oxygen mobility may have accelerated the surface oxidation reactions of carbon by reactive oxygen species, thus, inhibiting carbon growth on the catalyst surface.     

High-temperature reactor for hydrogen production by partial oxidation of hydrocarbons

Today, conversion of hydrocarbons is one of the most common hydrogen production technologies. This paper presents a design of a high-temperature reactor — the main component of a hydrogen production unit using partial oxidation of hydrocarbons — as well as a physical model of gas generation. It also presents a schematic diagram of an experimental setup as well as results of experimental studies on steady-state modes of partial oxidation in the combustion chamber of a high-temperature reactor for various hydrocarbon feed/oxidant combinations. In the course of the study, we identified patterns that describe how the excess oxidant ratio affects the composition of products of incomplete combustion of hydrocarbons to obtain hydrogen-containing gas of the required composition and parameters for hydrogen production. We propose a method to calculate nominal geometric dimensions of a high-temperature reactor, which makes it possible to estimate its weight and size at the design stage. The paper presents results of experimental studies confirming the adequacy of the proposed method.     

Influence of a reaction mixture streamline on partial oxidation of methane in an asymmetric microchannel reactor

Partial oxidation of methane (POM) has been tested in an asymmetric microchannel reactor with different inlet configurations. One inlet of the reactor provided successive splitting of an inlet flow into parallel channels, whereas the opposite inlet allowed the inlet flow to enter the parallel channels simultaneously. It was found that concentrations of carbon monoxide and carbon dioxide changed by 20–30% and the conversion of methane changed by 5–20%, depending on the rate and direction of the inlet flow. The hydrogen production rate practically did not depend on the inlet configuration and equaled 15 l/h at the inlet flow rates from 600 to 1400 cm³/min and at the methane conversion of 80%. The data obtained demonstrated that the use of different operating modes of the asymmetric microreactor allows changing the composition of produced syngas.     

Hydrogen production by glycerol reforming in a two-fixed-bed reactor

A two-stage fixed bed system was used in the hydrogen production from glycerol reforming. The calcined dolomite catalyst was used in the first fixed bed, and the Nickel-based catalyst was used in the second fixed bed to produce hydrogen from the glycerol steam reforming. The results showed that the hydrogen yield and carbon conversion gradually increased with the temperature increasing. When the temperature exceeded 800 °C, the growth rate of hydrogen yield and carbon conversion decreased. As the space velocity increased, the hydrogen yield and carbon conversion gradually decreased. When the space velocity was greater than 2 h^?1, the decline rate of hydrogen yield and carbon conversion decreased rapidly. As the water-to-carbon ratio (S/C) increased, the hydrogen yield and carbon conversion gradually increased. The growth rate of hydrogen yield and carbon conversion became smaller when the S/C was more than 5. Compared with the single-stage fixed-bed reactor, the utilization of two-stage fixed-bed catalytic reaction system can not only increase the hydrogen yield and carbon conversion, but extend the life of the Nickel-based catalyst. Under the optimal reaction conditions, the hydrogen yield is as high as 84.3%, and the carbon conversion is as high as 88.23%.     

Enhancement of pure hydrogen production through the use of a membrane reactor

Pure hydrogen production is of great interest as it is an energy carrier which can be used in PEM fuel cells for power production. Methane Steam Reforming (MSR) is commonly used for hydrogen production although the produced hydrogen is not free of other components. Membrane Reactors (MR) enable a pure hydrogen product stream and allows the reaction to take place at significantly lower temperatures (lower than 550 °C) than in conventional reactors (greater than 800 °C) with comparable methane conversion. This is achieved by hydrogen removal through a permselective Pd–Ag based membrane that cause a favorable shift in chemical equilibrium towards hydrogen production. In the present study, a two-dimensional, nonlinear, and pseudo-homogeneous mathematical model of a catalytic fixed-bed membrane reactor for methane steam reforming over a nickel-based foam supported catalyst is presented. Simulated results referring to the distribution of species, methane conversion, temperature and hydrogen flowrate along the reactor for different radial positions are obtained and analyzed. The performance of structured catalyst and catalyst supported on foam configurations under the same operating conditions is also studied. Experimental results for the membrane facilitate the identification of suitable operating conditions.     

Effect of ruthenium addition on molybdenum catalysts for syngas production via catalytic partial oxidation of methane in a monolithic reactor

Hydrogen is mainly produced from hydrocarbon resources. Natural gas, mostly composed of methane, is widely used for hydrogen production. As a valuable feedstock for ‘Fischer–Tropsch’ (FT) process and ‘Gas to Liquids’ (GTL) technology, syngas production from catalytic partial oxidation of methane (CPOM) is gaining prominence especially owing to its more desirable H₂/CO ratio; relatively less energy consumption, and lower investment, compared to steam reforming processes (SMR), the leading technology.In the present study, effect of ruthenium (Ru) addition on molybdenum (Mo) catalysts for syngas production from methane (CH₄) via partial oxidation in a monolithic reactor was investigated. Mo based catalysts supported on Nickel (Ni) and Cobalt (Co) metal oxides and Ni-Co bimetallic oxides and their Ru added versions were developed, characterized, and tested for performance in a monolithic type reactor system. Catalyst activity was investigated in terms of H₂ and CO selectivity, CH₄ conversion; and CO₂ emission and it is concluded that addition of Ru over the structure led to increase in catalytic activity and reduction in carbon deposition over the catalyst surface.     

Transient reaction and exergy analysis of catalytic partial oxidation of methane in a Swiss-roll reactor for hydrogen production

Catalytic partial oxidation of methane (CPOM) is a promising method for hydrogen production with autothermal reaction. To figure out the unsteady reaction characteristics of CPOM in a Swiss-roll reactor along with heat recirculation, a numerical method is employed to simulate the transient reaction dynamics, with emphasis on energy recovery using exergy analysis. Three different gas hourly space velocities (GHSVs) of 5000, 10,000 and 50,000 h⁻¹ with the condition of atomic O/C ratio of 1 are considered. The predictions indicate that increasing GHSV substantially shortens the transient period of chemical reactions; however, it also reduces the methane conversion, as results of more reactants sent into the reactor and shorter residence time of the reactants in the catalyst bed. Within the investigated range of GHSV, the methane conversion with energy recovery at the steady state is larger than 80%, much higher than the reaction without heat recovery. The selectivities of H₂ and CO in the product gas are always larger than 90%. The exergy recovery is in the range of 66–80%, implying that over two-third useful work contained in the product gas can be reused to preheat the reactants in the reactor, thereby enhancing the performance of CPOM.     

Characteristics of combined carbon dioxide reforming with partial oxidation of methane to produce hydrogen in the membrane reactor

Thermodynamic equilibrium constant method and mathematical model are used to analyze the investigating effects of temperature, α[oxygen‐methane molar ratio] and β [carbon dioxide‐methane molar ratio] on characteristics of oxidative CO₂ reforming of methane reaction over Ni/Al₂O₃ catalysts to produce hydrogen in the membrane reactor. While keeping temperature at 1100 K, the membrane reactor is no longer useful to separate hydrogen when α > 0.6 for hydrogen in reaction side is no longer to permeate side. When increasing β, the methane conversion goes up firstly until the β is 1.3, which is higher than the inflection point at 1.1 in the model prediction. The hydrogen yield peaks at β = 0.5 in permeate side. Increasing the temperature or reducing the β will cause the molar ratio of H₂/CO increase. However, changing α has no significant effect on adjusting the molar ratio of H₂/CO. By establishing equilibrium reaction model, the system performance can be accurately predicted. Copyright © 2016 John Wiley & Sons, Ltd.     

Calcium silicate-based catalytic filters for partial oxidation of methane and biogas mixtures: Preliminary results

Development and testing of catalytic filters for partial oxidation of methane to increase hydrogen production in a biomass gasification process constitute the subject of the present study. Nickel, iron and lanthanum were coated on calcium silicate filters via co-impregnation technique, and catalytic filters were characterized by ICP-MS, XPS, XRD, TEM, TGA, TPR and BET techniques. The influences of varying reaction temperature and addition of Fe or La to Ni-based catalytic filters on methane conversion, and hydrogen selectivity have been investigated in view of preliminary results obtained from reactions with 6% methane-nitrogen mixture, and catalytic filters were tested with model biogas mixtures at optimum reaction temperature of each filter which were 750 °C or 850 °C. Approximately 93% methane conversion was observed with nearly 6% methane-nitrogen mixture, and 97.5% methane conversion was obtained with model biogas containing CH₄ which is 6%, CO₂, CO, and N₂ at 750 °C. These results indicate that calcium silicate provides a suitable base material for catalytic filters for partial oxidation of methane and biogas containing methane.     

Simulation of methane conversion to syngas in a membrane reactor. Part II: Model predictions

A one-dimensional non-isothermal model was employed in the simulation of partial oxidation of methane to syngas in a dense oxygen permeation membrane reactor. The model predicts that if methane is consumed completely in the reactor, a temperature runaway occurs. The reactor inlet temperature is chosen as a major factor to demonstrate the correlativity of the reactor performance and this phenomenon. A borderline inlet temperature (BIT) is defined. Simulation results showed that when the reactor inlet temperature approaches this value, an optimized reactor performance is achieved. This temperature increases with the increase of the air flow rate and carbon space velocity. The surface exchange kinetics at the oxygen-rich side has a small effect on this temperature, while that at the oxygen-lean side has a significant effect.     

Increased hydroxyl concentration by tungsten oxide modified h-BN promoted catalytic performance in partial oxidation of methane

Hexagonal boron nitride (h-BN) as a layered inorganic nonmetallic material has been widely used. Hydrogen peroxide (H₂O₂) modification can trigger exfoliation and afford abundant B–OH active sites at edge of h-BN, which can enhance methane activation ability. Introducing tungsten oxide (WO₃) to h-BN produces a similar effect, because doping WO₃ into h-BN resulted in electron transfer to N, inducing fracture of B–N bond, resulting in N vacancy (triboron center), exposing more B sites and promoting the generation of B–OH. Significantly, the introduction of WO₃ on the modified h-BN dramatically increased the concentration of B–OH compared with the unmodified h-BN, because H₂O₂ modification weakened B–N bond. By means of XRD, TEM, XPS,EPR, FT-IR, it is proved that the high concentration of B–OH active sites contributed to activating C–H bond, thus methane conversion and CO and H₂ selectivity were significantly improved.     

Oxygen feeding strategies for methane ATR

The performance of different reactor designs for methane autothermal reforming (ATR) with diverse options of O₂ feeding is comparatively explored. The designs under consideration include a single bed reactor with O₂ feed at the inlet, multibed reactors in series with inter-bed oxygen injection, and a multitubular membrane reactor with O₂ feeding through the porous wall.The distribution of O₂ leads to low O₂ concentrations in the reaction mixture and less severe thermal conditions. The evolution of methane reforming and combustion reactions proceeds in parallel due to a suitable degree of reduction of the Ni catalyst. Particularly, the membrane reactor can produce H₂ in a more distributed way along the reactor. The leakage of O₂ at the membrane reactor outlet can be prevented with a final section of a non-porous wall. The modified membrane reactor demonstrates flexibility to carry out the methane ATR with lower temperatures without deterioration of H₂ yield.     

Partial oxidation of ethanol in a membrane reactor for high purity hydrogen production

Partial oxidation of ethanol was performed in a dense Pd–Ag membrane reactor over Rh/Al₂O₃ catalyst in order to produce a pure or, at least, CO_x-free hydrogen stream for supplying a PEM fuel cell. The membrane reactor performances have been evaluated in terms of ethanol conversion, hydrogen yield, CO_x-free hydrogen recovery and gas selectivity working at 450 °C, GHSV ∼ 1300 h⁻¹, O₂:C₂H₅OH feed molar ratio varying between 0.33:1 and 0.62:1 and in a reaction pressure range from 1.0 to 3.0 bar. As a result, complete ethanol conversion was achieved in all the experimental tests. A small amount of C₂H₄ and C₂H₄O formation was observed during reaction. At low pressure and feed molar ratio, H₂ and CO are mainly produced, while at stronger operating conditions CH₄, CO₂ and H₂O are prevalent compounds. However, in all the experimental tests no carbon formation was detected. As best results of this work, complete ethanol conversion and more than 40.0% CO_x-free hydrogen recovery were achieved.     

Hydrogen production by steam methane reforming in a membrane reactor equipped with a Pd composite membrane deposited on a porous stainless steel

With the aim of producing hydrogen at low cost and with a high conversion efficiency, steam methane reforming (SMR) was carried out under moderate operating conditions in a Pd-based composite membrane reactor packed with a commercial Ru/Al₂O₃ catalyst. A Pd-based composite membrane with a thickness of 4–5 μm was prepared on a tubular stainless steel support (diameter of 12.7 mm, length of 450 mm) using electroless plating (ELP). The Pd-based composite membrane had a hydrogen permeance of 2.4 × 10^?3 mol m^?1 s^?1 Pa^?0.5 and an H₂/N₂ selectivity of 618 at a temperature of 823 K and a pressure difference of 10.1 kPa. The SMR test was conducted at 823 K with a steam-to-carbon ratio of 3.0 and gas hourly space velocity of 1000 h^?1; increasing the pressure difference resulted in enhanced methane conversion, which reached 82% at a pressure difference of 912 kPa. To propose a guideline for membrane design, a process simulation was conducted for conversion enhancement as a function of pressure difference using Aspen HYSYS^®. A stability test for SMR was conducted for ～120 h; the methane conversion, hydrogen production rate, and gas composition were monitored. During the SMR test, the carbon monoxide concentration in the total reformed stream was <1%, indicating that a series of water gas shift reactors was not needed in our membrane reactor system.     

Abundant hydrogen production over well dispersed nickel nanoparticles confined in mesoporous metal oxides in partial oxidation of methane

To improve the stability of Ni catalysts and employ reactive oxygen species in reducible metal oxides, the Ni nanoparticles were confined within mesoporous metal oxides (La₂O₃, Yb₂O₃, ZrO₂, CeO₂) via evaporation-induced self assembly technique utilizing 3D honeycomb-like silica as substrate for partial oxidation of methane (POM). Compared with supported catalysts, the prepared catalysts showed superior catalysts stability especially 3D honeycomb-like ZrO₂ and CeO₂ supported Ni catalysts (Ni/3HL-ZrO₂-SiO₂ and Ni/3HL-CeO₂-SiO₂) due to confinement effect and strong interaction between Ni and metal oxides. CH₄ conversion reached 90%–92%. Outstanding catalytic activity was attributed to highly dispersity of active metal. More importantly, abundant hydrogen production was observed over mesoporous CeO₂, ZrO₂ supported catalysts and the ratio of H₂/CO changed from nominal value 2 to 3. DFT theoretical calculations illuminated structural defect sites of reducible support like CeO₂, ZrO₂ afforded generation of surface hydroxyl group, which can be regenerated by activation of water and reoxidation of CeO₂, ZrO₂. Hydroxyl group was beneficial to accelerate greatly water gas shift reaction, promoting the production of hydrogen. This may provide a strategy to regulate production composition of POM to expand its downstream process.     

A comparative study of molybdenum phosphide catalyst for partial oxidation and dry reforming of methane

Molybdenum phosphide (MoP) was firstly used as a catalyst for partial oxidation of methane (POM) and its catalytic performance for POM was compared with that for dry reforming of methane (DRM). It was found that the MoP phase was the dominant active site in POM and DRM reactions, and the activity would gradually decrease when more and more MoP was converted to Mo₂C phase (non-dominant active site) and then rapid deactivation would occur due to bulk oxidation of catalyst. The redox type mechanism over MoP catalyst was vitally important to keep its structure reasonably well during methane reforming reactions. The MoP catalyst revealed a higher catalytic stability in POM than in DRM, attributing to the higher H₂ yield obtained in POM, which can promote and maintain the redox cycle of catalyst.     

Confining Ni nanoparticles in honeycomb-like silica for coking and sintering resistant partial oxidation of methane

3D honeycomb-like silica surrounded by ZrO₂ layer (3HL-ZrO₂-SiO₂) was prepared via sol-gel coating method. The average cell diameter of prepared material is about 10 nm. The highly dispersed Ni nanoparticles were immobilized to cell of honeycomb by impregnation method. The synthesized catalysts were characterized by SEM, TEM, XRD, H₂-TPR/TPD, TGA and N₂ adsorption-desorption techniques. Contributed by confinement of honeycomb-like silica, the Ni/3HL-ZrO₂-SiO₂ catalyst showed superior anti-sintering and coking ability compared with conventional catalysts. Further, improving the oxygen storage capacity from ZrO₂ and highly dispersed active-sites afford excellent catalytic activity. CH₄ conversion up to 90%–92% was obtained. The blocking effect of honeycomb cell endowed outstanding sintering resistance referring to Ni based catalysts.     

Experimental investigation on the partial oxidation of methane with the effect of shrunk structure

Hydrogen energy is an ideal clean energy to solve the expanding energy demand and environmental problems caused by fossil fuels. In order to produce hydrogen, a double-layer porous media burner with shrunk structure was designed to explore the partial oxidation (POX) of methane. And the combustion temperature, species concentration and reforming efficiency were studied under different shrunk parameters and operating conditions. The results indicated that the shrunk structure greatly influenced the flame position and temperature distribution. The flame moved to the downstream section with the decreasing of the inner shrunk diameter and the increasing of the shrunk height. When the diameter of the filled Al₂O₃ pellets was 8 mm, the hydrogen yield reached the highest value of 43.8%. With the increasing of equivalence ratio, the reforming efficiency increased first and then decreased, and the maximum value of 53.0% was reached at φ = 1.5. However, the reforming efficiency and axial temperature kept increasing when the inlet velocity increased from 10 to 18 cm/s. The corresponding results provided theoretical reference for the control of flame position and species production by the design of shrunk structure in porous media burner.